O
n the morning of Aug. 29, 2005, the thirdstrongest hurricane ever recorded to hit the
United States rolled across Louisiana and
Mississippi, creating a massive clean-up and reconstruction challenge. The force quickly became widely
known as Hurricane Katrina. Destruction from the
hurricane was seen everywhere; in the city of New
Orleans, much of which is situated below sea level,
flooding from breached levees proved catastrophic.
Recognizing the critical importance of the levee
ern shore. The project started at the 17th Street
Canal and extended east to the Inner Harbor
Navigational Canal, and included the levee protection system.
Our company, Martin & Whitacre Surveyors &
Engineers Inc. (Muscatine), was subcontracted by
Stanley Consultants to produce 3D laser scan surveys for the flood gates, seawalls and structures
of the significant site. For this project, we used a
new Leica Geosystems (Norcross, Ga.) HDS3000
Scanning
the Levees
Laser scanning technology
plays critical role in mapping
damage from Hurricane Katrina.
by Gary Whitacre, pls
With a Leica Geosystems HDS3000 laser scanner, Martin & Whitacre Surveyors
& Engineers Inc. of Muscatine, Iowa, produced 3D surveys of the flood gates,
seawalls and structures in New Orleans following Hurricane Katrina.
system for the city’s protection, the U.S. Army Corps
of Engineers (USACOE) worked with a number of
surveying companies to map the damaged levees and
related structures as a first step toward improving
and strengthening these vital protective barriers.
The Rock Island District of the USACOE contracted with Stanley Consultants, an engineering,
environmental and construction services provider
located in Muscatine, Iowa, to map a six-mile
stretch of Lake Pontchartrain along the southeast26
August 2007 | Point of Beginning | www.pobonline.com laser scanner. Our crew consisted of my son Seth,
a land surveyor intern, and me.
To aid us in mapping the remaining earthen
levees and collecting utility information, we subcontracted C.H. Fenstermaker of Lafayette, La. The
utility data was captured primarily using RTK GPS,
while the topography was captured using a Leica
ScanStation. (For details on Fenstermaker’s work
in New Orleans, read “Aiding the Katrina Recovery,”
POB, October 2006.)
Holding Control
Daily Work
Working in post-Katrina New Orleans presented a number of
interesting challenges. One was control. Existing survey control monuments were known to be subsiding in the wake of
post-Katrina flooding. The USACOE Interagency Performance
Evaluation Task Force determined that the most stable of the
existing monuments was a point called ALCO, a bronze triangulation station disk set in the massive concrete seawall; therefore, project specifications were written so that ALCO would be
held as the primary control point for all work in that area. This
Our first task on location was to hold a brief planning session
to determine where we were going to set up the scanner, how
many setups we would need, what the field of view would be
and the desired point density. We used a 1-megapixel camera
on the scanner to take a digital picture of the entire project
site. From that image we decided which areas we would take
broad scans and which areas we would take dense scans.
Where we came across flat walls, for instance, we didn’t need
much information and could make do with less density. We
zeroed in to capture high-density scans of
various details, such as hinges on the gates
and construction joints. Since the time it takes
to complete a given scan is determined by the
field of view and the density of points, the ability to vary these factors on-the-fly gave us a lot
of flexibility to spend more time on those areas
that needed extra attention.
also meant that every surveyor onsite was scrambling to work
from one common point. At one particular time, we counted
10 different survey crews working in the designated area. And
many of them were utilizing ALCO for static observations or
RTK, which typically involved setting up on the point for an
entire day, preventing others from using it.
ALCO was set in 1931 by the U.S. Coast and Geodetic Survey.
Its current vertical datum at the time of our work was NAVD88
(2004.65) and horizontal datum NAD83 (1992), Louisiana South
Zone State Plane Coordinate System.
When using ALCO as a single control point, we held it vertically and ran a series of closed loops each day using a Leica
NA3003 digital level and barcode rods all the way to the east
end and back through about 15 control points that were set in
the seawall. Those points were also used in a horizontal control survey using static GPS and ALCO. Additionally, an OPUS
solution was run on those points for a check, so the control
surveys that we completed, both vertical and horizontal, and
the control points that will be set in the future, will be used as
control for the reconstruction project.
Above: Martin & Whitacre’s scanner was often mounted on their
¾ ton Chevrolet crewcab pickup truck equipped with a hydraulic
leveling system, giving them an instrument height of about 11 ½ ft.
Right: Seth Whitacre (seated) and Gary Whitacre examine scan data
taken at Bayou St. John’s in New Orleans. Debris and overgrown
vegetation often made a clear line of sight difficult.
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A 3D model (top), point cloud
(middle) and point cloud with model
overlay (bottom) of Bayou St. John’s
in New Orleans.
On a typical day, we were able to complete anywhere from two to six scans,
including our control work. Every setup
and every situation was different. For
some shots we were required to operate
in confined spaces, which made it difficult to set up the scanner. To get a higher
view, we often had to mount the scanner
on our ¾ ton Chevrolet crewcab pickup
truck equipped with a hydraulic leveling
system. When working from the truck,
we had an instrument height of about
11 ½ ft, giving us a big advantage over
the normal 5-6 ft of elevation. On one
occasion, we set up on a balcony at the
harbor master’s building in the Orleans
Marina so we could have a view down
between the condominiums and the
seawall to capture a small courtyard.
Another time we had to set the scanner
on top of the seawall.
From the registered point cloud,
topographic information was extracted to create planimetrics (horizontal
data of mapping features) for the
mapping, as well as contours, profiles
along the toe and top of the walls
and cross sections at 500-ft stations.
In addition to the basic mapping
information, we created 3D models
of all the walls and the 17 flood gates
throughout the six-mile project. Leica
Geosystems HDS Cyclone software
was used to create the 3D models,
and will aid in the design of the new
flood protection system.
Final deliverables included 34
sheets of 100-scale topographic mapping of the six miles of levee protection system, as well as profiles of the
top and toe of all slopes on the levee,
cross sections at 500-ft intervals, utility surveys of the entire six-mile stretch
and digital terrain models.
The Six-Mile Point Cloud
A Scanning Workhorse
A point cloud was required for 3,000
ft on the west end of the project in the
vicinity of the Orleans Marina, which
included more than 2,000 ft of a continuous flood wall and seven flood gates.
We also provided high-definition point
cloud data for an additional 10 flood
gate structures along the six miles of the
levee protection system.
Once the initial control surveys were
completed, Fenstermaker teams utilized
the levee as a baseline and occupied stations at about 100 m intervals to capture
the terrain with the ScanStation. This
system of intervals created an overlap of
data collected, which was registered to
create a five-mile point cloud. The result
of this combined effort was a six-milehigh density XYZ database.
The HDS3000 proved to be a real
workhorse on this complex and difficult job. Since our company was
one of the first to place an order for
the HDS3000 when it was introduced in
2003, we already had considerable experience working with this instrument on
numerous scanning projects. One of the
greatest advantages of the laser scanning system on this particular project
was the complete capture of anything
in the field of view. The high density
XYZ data along with the digital photo
image was invaluable for documenting the existing conditions. We were
able to leave the project site and return
home almost a thousand miles away
with complete confidence knowing that
no information was left uncollected.
When it comes to capturing detailed
information on a complex structure like
this, laser scanning technology offers
clear advantages over other surveying
ALCO, a bronze triangulation station disk
set in the massive concrete seawall, was
held as the primary control point for all
work in the area and often caused delays
when other survey crews were using it.
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August 2007 | Point of Beginning | www.pobonline.com Working in Post-hurricane Conditions
Working in New Orleans after Hurricane Katrina proved difficult. Having never been to the city before, Whitacre and
his son Seth initially had a lot of trouble finding their way
around. The category 5 storm eradicated many street signs
and twisted one-way signs to point in the wrong direction. It
took them a while to get oriented.
An unforeseen difficulty the Whitacres encountered on
the project was overgrown vegetation. They needed a clear
line of sight for the laser scans. Although they did get good
cooperation when asked to have the vegetation cleared, they
sometimes had to cut the weeds and high grass themselves
before scanning could begin.
Vibration from the large pumping station in the vicinity of
the 17th Street Canal and from pile-driving activity nearby
was another obstacle, causing the team to lose about threequarters of a day’s work because they initially did not understand why their data was so bad. They eventually caught on
to the vibration impact and rescheduled work around the
pump testing and construction work.
tools. There is no comparison in terms of speed and accuracy.
Without this technology we would have had to take a large
number of single measurements and connect the dots—and
probably do a lot of hand sketches on a clipboard.
I can truthfully say that I would never consider taking on a job
of this type or magnitude without 3D laser scanning. I believe,
especially from this experience, that high-density laser scanning
will have as big an impact on surveying as the advent of RTK GPS
a few years ago.
Gary Whitacre, PLS, is president of Martin & Whitacre Surveyors &
Engineers Inc. of Muscatine, Iowa. He is a licensed land surveyor in Iowa,
Illinois, Missouri and Wisconsin.
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